1. Field of the Invention
The present invention relates to a vehicle-mounted electronic control apparatus adapted to be applied, for example, to an engine control apparatus, a vehicle cruise control apparatus, etc. More particularly, it relates to a vehicle-mounted electronic control apparatus capable of reducing a control load on a control microprocessor thereby to enhance control response as well as the reliability of a backup memory by improving how to check the abnormality of the backup memory used with the control microprocessor.
2. Description of the Related Art
In general, a vehicle-mounted electronic control apparatus includes a main power supply circuit that is supplied with electric power from a vehicle-mounted or on-board battery to generate a first stabilized control voltage upon closure of a power supply switch, a microprocessor (control CPU) to which electric power is fed by the main power supply circuit, an auxiliary power supply circuit which is directly fed with electric power from the on-board battery to generate a second stabilized control voltage without passing through the power supply switch, and a volatile backup memory to which electric power is always supplied from the auxiliary power supply circuit or the main power supply circuit.
The control CPU controls a variety of kinds of electric loads in response to the contents of a nonvolatile control memory (e.g., control programs and reference control constants) and the operating states of various input sensors.
The backup memory stores therein learning correction variation value data with respect to the reference control constants in the nonvolatile control memory. A partial area or the whole area of a RAM memory is used as the backup memory, and for instance, learning data to improve driving performance, calibration value data to improve control precision, abnormality occurrence frequency data according to abnormal code numbers, etc., are given as the data stored in such a memory area.
These pieces of storage data have the possibility that their storage contents are changed or lost by the influences of abnormal voltage reduction of the on-board battery, power supply interruption or cut-off upon battery replacement, abnormal noise during operation, etc. Accordingly, pieces of critical or important data are transferred to and stored in a electrically writable nonvolatile data memory so that they can be used as initialization data at the time of data loss.
Here, note that the nonvolatile data memory takes the time required for writing longer than a RAM memory does, and has a limitation to the number of times or frequency of rewritings. Thus, in general, batch transfer writing is executed before a power supply interruption after an engine to be controlled is stopped.
In addition, if data loss occurs by any chance for data of such low significance as can be learned and corrected again, the learning correction variation value data is initialized as initialization data, and the reference control constants stored in the nonvolatile control memory are used as they are, so that it becomes unnecessary to perform data transfer and storage to the nonvolatile data memory, thereby making it possible to reduce or suppress the storage capacity needed in the nonvolatile data memory.
Under such a technical background, it is always required to check whether the contents of the backup memory are normal, and if abnormal, to quickly perform initialization processing.
However, in general vehicle-mounted electronic control apparatuses, as an abnormality detection means for checking or inspecting the contents of the backup memory, there exists no versatile means capable of performing a full check on the backup memory in a short time, and it is known that an excessive emphasis placed on the abnormality check influences the control performance of the microprocessor.
There has been proposed, as one of conventional typical abnormality detection means, an electronic control apparatus that is provided with a backup memory {see, for instance, a first patent document (Japanese patent application laid-open No. H6-74087 (FIG. 3 and Summary))}. The conventional apparatus described in this first patent document includes a backup memory that is always or constantly supplied with battery power and stores pre-specified check data that is irrelevant to control, a control data storage section that stores control data to be updated during the execution of control into the backup memory, an inverted data storage section that stores inverted data which is generated by inverting each bit of the control data into the backup memory when the control data is stored by the control data storage section, a determination section that makes a comparison between the control date stored in the backup memory and the inverted values of the inverted data so as to determine whether they coincide with each other, and an initialization section that writes initial values into the backup memory when the determination section determines that the control data and the inverted values of the control data do not coincide with each other.
Also, the above-mentioned initialization section includes a first section that rewrites the check data into false check data (i.e., values different from the pre-specified values), and a second section that rewrites the check data into the pre-specified check data in place of the false check data after completion of the initialization in which the initial values are written.
Further, the above-mentioned first patent document discloses a mirror check method for comparing the pieces of inverted data with each other, and a keyword verification method using specific check data, whereby the specific check data is replaced from the false data into normal data in response to the completion of initialization, so that the state of interruption of the initialization can be detected, thereby performing initialization in a reliable manner.
In contrast to this, an apparatus and a method for initializing electronic equipment have also been proposed as another prior art {see, for instance, a second patent document (Japanese patent application laid-open No. H7-36574 (FIG. 1 and Summary))}.
According to this second patent document, the initialization apparatus for electronic equipment includes a memory backed up by a voltage served from a power supply (battery), a detection section that detects when the voltage served to the memory reduces below a predetermined value, a storage section that stores information indicating an undervoltage state detected by the detection section, and a control unit that checks the contents of the storage section upon power-on of the electronic equipment, and executes preset initialization processing when information indicating the undervoltage state is stored.
In the case of the conventional apparatus described in the above-mentioned second patent document, the content of the backup memory itself is not checked but instead the presence or absence of an undervoltage abnormality, which becomes a cause to generate abnormal data, is detected, and if an undervoltage abnormality occurs, the backup memory is initialized irrespective of the content thereof.
In the conventional vehicle-mounted electronic control apparatuses, particularly in case of the above-mentioned first patent document, even in a situation where the contents of the backup memory are not reliable because of the presence of the history of a connection interruption or an abnormal voltage reduction of the on-board battery, if no change occurs by chance in the specified check data, there arises a need to verify the inverted data related to the multitude of pieces of storage data, thus posing the problem of requiring a large period of time for abnormality check.
In addition, in case of the above-mentioned second patent document, there is a problem that it is impossible to cope with an abnormality in the backup memory due to a noise-induced malfunction, etc., other than a cell voltage failure, thus resulting in an inability to achieve abnormality detection with high reliability.